Process for the removal of sulfur from ferrous metals



Patented May 23, 1950 PKGCESS FQR THE REMOVAL OF SULFUR FROM FERROUS METALS James Fernando J ordan'. Huntington Park,,Calif.

No'Drawing. Application'september 8, 1948,

Serial No. 48,310- r Claims. (01., li -55.)

My invention relates tothe desulphurization of ferrous metals.

This application is a continuation-impart. of my copendi-ng application." Serial No. 25,783, filed on May 7, 19 18, now abandoned'.

I have discovered that reagent slags composed of, or containing: sodium sulphide, potassium sulphide, or aluminum sulphide, are efiicient desulphurizers of molten ferrous metals. This discovery meets a need within ferrous refining metallurgy; for, more efiicientlow-melting point e lphuri a ents are in demand within said metallurgy.

Thus, in tests that. Imade with. a molten pig iron containing 1.09% manganese and 0.045%v sulphur, I found thatit was possible to lower said sulphur to 0.007% with molten sodium sulphide; to 0.010 with a slag composed of 75% potassium sulphide and 25%. aluminum. sulphide; and; to. 0.005% with a slag composed of aluminum sulphide.

The slags from these tests indicated that the sulphur moved into said slags as manganese sulphide. It is therefore believed that the reaction mechanism consists of the extraction process wherein MnS(in the metal) MnS(in the slag) (1) That the presence of manganese within the molten pig iron is not required for efiicient desulphurization with these sulphide reagents was shown in tests that I made with another molten pig iron that contained 4.25% carbon, 1.25% silicon, 0.08% manganese and 0.097% sulphur. Sodium sulphide lowered the sulphur in this pig iron to 0.010 and the manganese to 0.06%, while aluminum sulphide lowered the sulphur to 0.010% and the manganese to 0.05%. Here, it may be assumed that the reaction mechanism is the extraction process where FeS(in the metal) FeS(in the slag) (2) These molten sulphides react with the oxygen in the air to form the corresponding sulphates. I protect the molten sulphides from such oxidation by sometimes covering the molten slag with powdered charcoal, and sometimes covering said molten slag with methane. The molten sulphides tend to fume, particularly the potassium sulphide. Fuming may be minimized by employing low extraction temperatures, and by employing the non-volatile-solute effect, wherein the boiling point of the sulphide is elevated by dissolving therein a solute that is non-volatile. When employing sodium or potassium sulphide, I use 2. 7 either aluminum or cale'= m sulphide to elevate the boiling point or the melt. other compounds". such as the corresponding oxides, may beemployed as the non-volatile solute.

Steel may be desulphurized with these sulphide reagents. Thus, in tests that I made with a,

molten steel containing 0.30% carbon, 0ig5 %.sili. con, 0.89% manganese and 0.039%. sulphur. I lowered the sulphur to 0.011% with a slaggopmposed of 90% aluminum sulphide and 10% aluminum oxide, and I lowered the sulphur to 0.012%. with a slag composed of aluminum sulphide, 10% aluminum oxide, 15% sodium sulphide and 15% potassium sulphide.

While I prefer sodium sulphide, or potassium sulphide, or aluminum sulphide, or combiner-I tions of these three sulphides, the use ofother similar sulphides is of-course permissible. Thus, as. previousl mentioned. I have employed cale i m phide in these reagent slaessandi I. have on occasion used beryllium sulphide as a substitute for aluminum sulphide. To be employed in my reagent slag, a sulphide must be essentially immiscible in the molten metal that is to be desulphurized; must be a solvent for the sulphides which are to be extracted from said molten metal; and must be the sulphide of a metal whose affinity for sulphur exceeds the afiinity for sulphur exhibited by the molten metal that is to be treated.

I have furthermore found that the addition of aluminum to the molten metal will greatly improve the efiectiveness of my reagent slags. Thus, in a test that I made with a molten iron containing 0.177% sulphur, I added a slight excess of aluminum to said molten iron before treating said iron with a molten sulphide slag consisting of aluminum sulphide and 10% aluminum oxide, said excess being figured on the basis of 3MnS+2Al Al-2S3+3Mn (3) This aluminum-treated metal showed 0.008% sulphur after said treatment with said slag. Without said aluminum addition to said metal, said slag was capable of lowering the sulphur content of said metal to 0.052%--the same weight of slag being employed in both tests, of course. In another test that I made with this molten iron containing 0.177% sulphur, I treated the aluminum-treated metal with a reagent slag consisting of 40% sodium sulphide, 40% potassium sulphide and 20% aluminum sulphide, with the result that the sulphur content of said molten iron was lowered to 0.012%.

Other tests that I have made have shown that the aluminum addition need not necessarily be in excess of the requirements predicted by Reaction 3; that is, I have obtained, for example, a marked improvement in my process when the aluminum addition was only 50% of the requirements predicted by Reaction 3. I have also noted that the addition of such elements as beryllium and zirconium to the molten metal improves the efficiency of my reagents, apparently in the same manner as the aluminum addition. It seems likely that the function of the aluminum addition relates to the conversion of the sulphur content of the molten metal into sulphur compounds whose solubility products are low.

My extraction process may be carried out in any refining vessel wherein two interacting metallurgical liquids may be entertained. The teapot ladle of the iron foundry may be used, for example. Such a ladle should be covered and should possess the means for maintaining a protective atmosphere over said sulphide slag.

Having now described several forms of my invention, I wish it to be understood that my invention is not to be limited to the specific form or arrangement of steps herein disclosed, except insofar as such limitations are specific in the appended claims.

I claim as my invention:

1. The method of removing sulphur from molten ferrous metal, which comprises: contacting said molten ferrous metal with a molten sulphide slag consisting essentially of a sulphide selected from the group consisting of sodium sulphide, potassium sulphide, aluminum sulphide and mixtures thereof; maintaining said molten sulphide slag in contact with said molten ferrous metal until said slag has lowered the sulphur content of said metal; and separating said molten ferrous metal from said molten sulphide slag.

2. The method according to claim 1 in which sodium sulphide is the principal desulphurizing agent in said molten sulphide slag.

3. The method according to claim 1 in which potassium sulphide is the principal desulphurizing agent in said molten sulphide slag.

4. The method according to claim 1 in which aluminum sulphide is the principal desulphurizing agent in said molten sulphide slag.

5. The method according to claim 1 in which aluminum is added to the molten sulphur-bearing metal before said metal is contacted with said molten sulphide slag.

JAIVBES FERNANDO JORDAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,425,701 Sem Aug. 15, 1922 1,658,879 Browne Feb. 14, 1928 1,982,959 Kuhlmann Dec. 4, 1934 2,110,066 Heuer Mar. 1, 1938 2,301,360 Brennan Nov. 10, 1942 FOREIGN PATENTS Number Country Date 685,623 Germany Dec. 21, 1939 OTHER REFERENCES Chemical Abstracts, volume 8, pages 1729 and Economic Geology, volume 28, pages 773-777 (1933).

Metals and Alloys," volume 10, page MA 18 (January) and page MA 84 (February), (1939). 

1. THE METHOD OF REMOVING SULPHUR FROM MOLTEN FERROUS METAL, WHICH COMPRISES: CONTACTING SAID MOLTEN FERROUS METAL WITH A MOLTEN SULPHIDE SLAG CONSISTING ESSENTIALLY OF A SULPHIDE SELECTED FROM THE GROUP CONSISTING OF SODIUM SULPHIDE, POTASSIUM SULPHIDE, ALUMINUM SULPHIDE AND MIXTURES THEREOF; MAINTAINING SAID MOLTEN SULPHIDE SLAG IN CONTACT WITH SAID MOLTEN FERROUS METAL UNTIL SAID SLAG HAS LOWERED THE SULPHUR CONTENT OF SAID METAL; AND SEPARATING SAID MOLTEN FERROUS METAL FROM SAID MOLTEN SULPHIDE SLAG. 